1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a technique for filling a contact hole formed in an interlayer dielectric film with a wiring (plug) made of aluminum (Al) or an aluminum alloy.
2. Description of the Related Art
In accordance with the development of high integration and size reduction in semiconductor devices, a contact hole formed in an interlayer dielectric film is also becoming smaller in size and coming to have a higher aspect ratio. As a method for forming a plug by filling the contact hole of a small size with a metal in order to establish a good electric connection in the wiring via the plug in the contact hole, there are known several methods such as the high temperature Al sputtering method, the high temperature Al reflowing method, the tungsten CVD method or the like. Among these, the high temperature Al sputtering method and the high temperature Al reflowing method are attracting people's attention because the contact hole can be filled with a low resistance material and, in addition, the wiring film and the plug can be formed at the same time, thereby leading to reduced costs, as compared with the tungsten CVD method.
The high temperature Al sputtering method is a technique of sputtering an Al-based material such as Al or an Al alloy with the substrate heated at 400 to 500.degree. C. to reflow the Al-based material so as to fill the contact hole formed in the interlayer dielectric film with the Al-based material for forming the plug.
If the contact hole is filled with an Al-based material for forming a plug to electrically connect a wiring film disposed on an interlayer dielectric film with a diffusion layer in a Si substrate, a junction leakage is generated due to a phenomenon called "spike" in which Al diffuses abnormally into the diffusion layer of the Si substrate. A barrier metal is required in order to prevent this leakage. Generally, a TiN film or a TiW film is used as the barrier metal. If the TiN film is to be used, a laminated structure of TiN/Ti is adopted so as to reduce the contact resistance of the plug.
Also, if an Al-based material film 17 is directly formed on a TiN film 16 in order to fill the contact hole with the Al-based material by the high temperature sputtering method, the reflowing of theAl-based material film is not sufficient. Therefore, voids 18 tend to be generated as shown in FIG. 2. Therefore, in order to improve the wettability of the barrier film, a Ti/TiN/Ti structure is adopted in which a Ti film is formed on the TiN film which is the barrier film.
However, as the size reduction develops to reduce the diameter of the contact hole to less than a half micron, the conventional TiN film does not provide a sufficient barrier property when the barrier film is formed by the sputtering method, because the thickness of the barrier film at the bottom of the contact hole is small.
Therefore, in order to increase the barrier property, Japanese Unexamined Patent Publication No. HEI 07(1995)-29853, for example, discloses a method of increasing the barrier property by treating the TiN film of the barrier film with nitrogen.
Namely, as shown in FIG. 3(a), an interlayer dielectric film 13 is formed on a Si substrate 11 having a diffusion layer 12 formed therein. A contact hole 14 is then formed in the inter layer dielectric film 13. Further, a Ti film 15 is formed thereon, followed by forming a TiN film 16, as shown in FIG. 3(b). Then, an annealing treatment is carried out in a nitrogen atmosphere to form a TiN reformed film 16a to increase the barrier property, as shown in FIG. 3(c).
Also, Japanese Unexamined Patent Publication No. HEI 05(1993)-259116 discloses a technique of adopting a Ti 20/TiON 19/Ti 15 structure including a TION film 19 having a high barrier property as a barrier film, as shown in FIG. 4.
The above-mentioned Japanese Unexamined Patent Publication No. HEI 07(1995)-29853 makes use of TiN as a wetting layer. However, if the contact hole is to be filled with an Al-based material, Ti is greatly excellent as a wetting layer.
However, if a Ti film is directly formed on the TiN film which serves as the barrier film, voids tend to be generated. This is due to the fact that the barrier film is oxidized to some extent during the barrier property improving process (an annealing treatment under an atmosphere containing nitrogen or under an atmosphere containing nitrogen and oxygen), so that the interface between the Al-based material formed on the barrier film and the Ti film is also oxidized, thereby degrading the wettability of the Ti film.
In Japanese Unexamined Patent Publication No. HEI 5(1993)-259116, Ti is formed as a wetting layer on the TiON film, so that Ti is oxidized to degrade the wettability, in the same manner as above.
Japanese Unexamined Patent Publication No. HEI 06(1994)-85084, for example, proposes a method for preventing the oxidation of Ti in the wetting layer. According to this method, a non-doped polysilicon film or an impurity-introduced polysilicon film is formed as an antioxidation film on the inner wall of the contact hole before the contact hole opened in the interlayer dielectric film is filled with an Al-based material.
However, these films have a high resistance, so that it is necessary to remove a portion of the film at the bottom of the contact hole in order to reduce the resistance of the plug in the contact hole. This involves complicated manufacturing steps.